Shawnee National Forest - Geology

Geology

During the Illinoian Stage (between 352,000 to 132,000 years ago), the Laurentide ice sheet covered up to 85 percent of Illinois. The southern margin of this ice sheet was located within what is now the area of the Shawnee National Forest. There are many points of interest marking the southern edge of the glacier. Some are located within the Forest boundary, others are on public land in proximity.

Little Grand Canyon is located within the Shawnee National Forest. This is accessible off Illinois Route 127 south of Murphysboro, Illinois. A small creek with a tiny watershed has carved an impressive rock canyon, more than 200 feet deep, leading down to the Big Muddy River. The southern edge of the ice sheet was just to the north of Little Grand Canyon. Blocks of ice slid off the face of the glacier, carried by enormous volumes of meltwater, to carve this tiny canyon. In the deep shade of the canyon are relict species of Arctic plants left over from its ancient origin.

Cedar Lake is an artificial lake formed by damming Cedar Creek. The lake is accessible off Illinois Route 127, south of Murphysboro, and off U.S. 51, south of Carbondale. In this area, the Illinoian Glacier climbed the Shawnee Hills at its southern margin. The glacier blocked the waterways flowing north down the hills. This drainage formed a creek running northwest along the face of the glacier. This became Cedar Creek, the watershed of which is extremely asymmetrical. While the watershed extends only a few thousand feet to the south, up the face of the terminal moraine, the creek is also fed by waterways extending miles to the south.

Within the area of the Shawnee National Forest, but not at this time US property, is Hicks Dome, an igneous feature in Hardin County, Illinois. This was formerly speculated to be the result of a hot spot, but some argue it was caused by a meteorite impact.